Crane assemblies are well known in the art and encompass various modifications in structure. Many arrangements are restricted to mounting on a vehicle and employ extremely large hydraulically actuated booms, masts, etc.
The portable arrangements are restricted in that they generally too require large apparatus and are somewhat limited in functional diversity.
Such known arrangements include the device disclosed in U.S. Pat. No. 4,241,837. The document discloses an articulated boom crane which is convertible to a straight boom crane arrangement. A secondary boom is coupled to a main boom and inclined adjustable extensible members. However, the conversion to a straight boom requires the user position stop plates on the structure, which requires considerable time and effort. Additionally, the crane is hydraulically operated and requires trained manipulation to effect proper operation.
U.S. Pat. No. 4,508,233 describes a compact crane having a telescopically adjustable mast and a pivotally linked permanent boom. Located within the permanent boom is a secondary boom which is adjustable within the permanent boom. This arrangement is useful for limited applications, since the apparatus is manually operable and requires extensive adjustment and securing prior to use.
Brown, in Canadian Patent No. 1,067,862, discloses an extension for main booms comprising a pair of boom extension sections. One of the sections, i.e. the first main boom is movable from a storage to operating condition and similarly the second boom is movable from a storage position adjacent the first main boom to an operating condition when extensible members extend the length of the boom.
Having regard to the limitations of the prior art arrangements, there exists a need for a mobile and portable light weight crane having components which may be readily converted from a storage position to an operational position using tension and further which may be fully rotated under load or no-load conditions. Applicant, with the present invention, addresses this need.